test: update Bruno test data for media items

Update Bruno API test collections with latest test data:

Bookhoard.yml environment:
- Update media_item_id to current database value after recent
  database recreation/schema updates

Create Media Rating test:
- Change test rating from 8 to 7 to test different rating value
  for validation

These are test infrastructure updates only, no application code changes.

bruno/environments/Bookhoard.yml

@@ -3,7 +3,7 @@ variables:
   - name: base_url
     value: http://localhost:8765
   - name: media_item_id
-    value: 02a535a4-19f8-43fa-b81b-89a226d19dd9
+    value: 18a08a9f-4683-4250-8eec-11983753b6dc
   - name: fake_book_id
     value: 123e4567-e89b-12d3-a456-426614174000
   - name: user_id

bruno/media-items/Create Media Rating.yml

@@ -13,7 +13,7 @@ http:
     type: json
     data: |-
       {
-        "rating": 8
+        "rating": 7
       }
   auth: inherit